1. Field of the Invention
The present invention relates to a disk driving apparatus for positioning and rotatively driving a disk for an SVF system (STILL VIDEO FLOPPY SYSTEM) or the like.
2. Description of the Prior Art
FIG. 3 shows a disk cartridge 1 for an SVF system capable of recording and reproducing a still picture signal and a disk driving apparatus 10 for driving a disk within the cartridge 1. FIG. 4 shows in section a prior art disk driving apparatus 10 of the described type.
As shown in FIG. 4, in the cartridge 1 for a disk for the SVF system, there are made holes 2a and 2b in the center of a case 2, and between the holes 2a and 2b is provided a hub 3. The disk D received in the case 2 is fixed at its center to the hub 3, and on the underside of the periphery of this hub 3, there is provided a yoke 4 of a magnetic material for attraction by a magnet.
On the other hand, the disk driving apparatus 10 is formed of a disk holding portion 11 and a motor 12 as shown in FIG. 4. In this apparatus, a pair of ball bearings 15 are fixed at their inner rings to a shaft 14 which is fixed to a chassis 13, and to the outer rings of the ball bearings 15 is fixed a bearing housing 16. In this prior art example, the upper peripheral surface of the bearing housing 16 is made into a centering peripheral surface 16a. The centering peripheral surface 16a is dimensioned so as to fit in the center hole 3a of the hub 3 within the disk cartridge 1 with virtually no clearance left therebetween. In the SVF system, since the data track recorded on the disk D must be scanned by a magnetic head with high accuracy, the centering peripheral surface 16a is required to be controlled within the order of a .mu.m in its rotational run-out tolerance and fit tolerance with the hub 3. At the upper end of the shaft 14, there is fixedly disposed a guide member 17. The underside of the guide member 17 is in abutment with the inner ring of the upper ball bearing 15, and the inner and outer rings of the upper and lower ball bearings 15 are provided with a pre-load in the direction of thrust by the guide member 17. Further, the peripheral surface of the guide member 17 is made into a taper surface 17a, and the center hole 3a of the hub 3 within the disk cartridge 1 is adapted to be guided by the taper surface 17a onto the above mentioned centering peripheral surface 16a. And, on the upper periphery of the bearing housing 16, there is disposed a center core 18, and on the interior of the upper portion of the center core 18 is disposed a hold magnet 19.
The yoke 4 formed integral with the hub 3 within the cartridge 1 is attracted by the hold magnet 19 so that the under side of the yoke 4 is brought into abutment with the upper side 18a of the center core 18. And, the center hole 3a of the hub 3 guided by the taper surface 17a is put on the centering peripheral surface 16a. Under such conditions, the disk D within the disk cartridge 1 is accurately positioned and held by the disk holding portion 11.
While there is provided a rotor magnet 22 fixed to a rotor 21 which is fixedly attached to the lower periphery of the bearing housing 16, there is provided a rotor yoke 25 fixed to the bearing housing 16 opposite to the rotor magnet 22. On the chassis 13, there is provided a base plate 23, and on this base plate 23 is mounted a stator coil 24 interposed between the rotor magnet 22 and the rotor yoke 25. In the motor 12, the rotor magnet 22 is rotatively driven by the current passed through the stator coil 24. And thereby, the hub 3 held at the upper portion of the bearing housing 16 is driven for rotation within the case 2 of the cartridge.
The case 2 of the cartridge as shown in FIG. 3 is provided with a shutter 5, and the disk D when the shutter 5 is open is exposed to outside so that the magnetic head (not shown) is enabled to make record or reproduction on the same.
Now, the hub 3 within the disk cartridge 1 is held by the centering peripheral surface 16a in the case of the above disk driving apparatus, and therefore, the centering peripheral surface 16a must be made of an excellent material in wear resistance. Since, however, the centering peripheral surface 16a has conventionally been formed integral with the bearing housing 16, it has been required in order to secure the wear resistance of the centering peripheral surface 16a that the entire bearing housing 16 is made of a wear resisting material. Further, the bearing housing 16 must be provided by machining with some positioning portions for attaching thereto the rotor 21, rotor yoke 25, and so on, in place, but when the housing has to be made of a hard material, the processability for providing such portions is deteriorated. Also, materials excellent in wear resistance are generally expensive, and therefore, it increases the manufacturing cost of the overall disk driving apparatus when the bearing housing 16 as a whole must be fabricated of such material.